Java技术篇·IO包·字符流

一、编码问题

见之前的博客：https://blog.youkuaiyun.com/womeng2009/article/details/84187262

二、文本和文本文件

Java中文本（char）是16位无符号整数，是字符的unicode编码（双字节编码）

文件是byte byte byte…的数据序列

文本文件指的文本（char）序列按照某种编码方案（utf-8、utf-16be、gbk）序列化为byte的存储结果

三、字符流（Reader/Writer）- 输入输出流的抽象类

字符的处理，一次处理一个字符。字符的底层仍然是基本的字节序列。

四、字符流的基本实现

InputStreamReader 完成byte流解析为char流，按照编码解析

OutputStreamWriter 提供char流到byte流，按照编码处理

程序示例：

package com.io;

import java.io.*;

public class IsrAndOsw {
    public static void main(String[] args) {
        Reader reader = null;
        Writer writer = null;
        try {
            reader = new InputStreamReader(
                    new FileInputStream("/Users/xxx/Downloads/io_test/random_file1.txt"), "gbk");
            writer = new OutputStreamWriter(
                    new FileOutputStream("/Users/xxx/Downloads/io_test/random_file2.txt"), "gbk");
            char[] readBuff = new char[1024];
            int b;
            while ((b = reader.read(readBuff, 0, readBuff.length)) != -1) {
                writer.write(readBuff, 0, b);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (writer != null) {
                try {
                    writer.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

FileOutputStream输出结果：

五、字符流之文件读写流

FileReader/FileWriter

缺点：不能指定编码。

程序示例：

package com.io;

import java.io.*;

public class FileRW {
    public static void main(String[] args) {
        FileReader fileReader = null;
        FileWriter fileWriter = null;
        try {
            //不能指定编码，如果跟项目编码不同，只能回归到InputStreamReader/OutputStreamWriter
            fileReader = new FileReader(new File("/Users/xxx/Downloads/io_test/random_file1.txt"));
            fileWriter = new FileWriter(new File("/Users/xxx/Downloads/io_test/random_file3.txt"));
            char[] buff = new char[1024];
            int b;
            while ((b = fileReader.read(buff, 0, buff.length)) != -1) {
                fileWriter.write(buff, 0, b);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fileReader != null) {
                try {
                    fileReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fileWriter != null) {
                try {
                    fileWriter.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

FileWriter输出结果：

六、字符流的过滤器

BufferedReader 可以readLine，一次读一行

BufferedWriter/PrintWriter 可以写一行（可结合PrintWriter操作）

package com.io;

import java.io.*;

public class BwAndBr {
    public static void main(String[] args) {
        BufferedReader br = null;
        BufferedWriter bw = null;
        PrintWriter print = null;
        try {
            br = new BufferedReader(new InputStreamReader(
                    new FileInputStream("/Users/xxx/Downloads/io_test/random_file1.txt"), "gbk"));
            bw = new BufferedWriter(new OutputStreamWriter(
                    new FileOutputStream("/Users/xxx/Downloads/io_test/random_file4.txt"), "gbk"));
            print = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
                            new FileOutputStream("/Users/xxx/Downloads/io_test/random_file5.txt"), "gbk")));
            String line;
            while ((line = br.readLine()) != null) {
                bw.write(line);
                bw.newLine();
                bw.flush();//必须刷新缓冲区

                //PrintWriter方式
                print.println(line);//带换行
                print.print(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (bw != null) {
                try {
                    bw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (print != null) {
                print.close();
            }
        }
    }
}

BufferedWriter输出结果：

PrintWriter输出结果：